This invention relates generally to devices for handling materials without contamination of the materials, and more particularly to a device which suppresses splashing of particles onto a semiconductor wafer.
The production of high quality semiconductor wafers requires the maintenance of clean wafer surfaces during processing. In particular, the avoidance of defects during the deposition of a monocrystalline (i.e., epitaxial) layer on a surface of the wafer requires the virtual absence of particles on the surface of the wafer. During the epitaxial layer deposition process, the wafer is held in the reaction chamber in a wafer pocket or compartment on a susceptor with one face directed outwardly of the compartment on which the epitaxial layer is to be deposited.
Occasionally, when the wafer is placed in the susceptor compartment, the impact of the wafer against the floor of the compartment is sufficient to cause disintegration of a layer of the semiconductor material on the susceptor around the point of contact left from a previous deposition process. Particles can also be generated when the wafer is removed from the compartment and a bridge of deposited semiconductor material between the wafer and the susceptor at the contact point is broken. Particles generated can be splashed onto the outwardly directed wafer face resulting in epitaxial defects such as hillocks, ESF's and spikes. The existence of these defects (often referred to as "light point defects" because of the procedure used to test for the defects) can greatly reduce the quality of the wafer, affecting the yield of wafers produced which meet specification. It is believed that splashing occurs as a result of the kinetic energy of the particles after they are broken away, the ascending flow of gas around the susceptor and over the outwardly directed face of the wafer, and/or the presence of a static charge which attracts the particles to the face of the wafer.
Prior efforts to reduce light point defects have not adequately remedied the problem. Training of the operator can result in a reduction of particle generation, but does not assure consistency of result, as significant particle generation may occur notwithstanding the skill of the operator. Many of the particles generated as described above are sufficiently large to survive acid gas (HCl) etching applied to the wafers just before the deposition of the epitaxial layer occurs. Different geometries of the wafer compartment in the susceptor and frequent etch back of semiconductor material deposited on the susceptor have also not been completely successful.